TEMPERATURE, PRESSURE, AND PERTURBER DEPENDENCIES OF LINE-MIXING EFFECTS IN CO2 INFRARED-SPECTRA .1. SIGMA[-PI BRANCHES

Experimental and theoretical results on the influence of line mixing o n the shape of infrared CO2 Q branches of importance for atmospheric a pplications are presented. Two Q branches of Sigma <-- Pi symmetry, wh ich lie near 618 and 720 cm(-1) and belong to the 10(0)0(II)<-- 01(1)0 (I) and 10(0)0(I) <-- 01(1)0(I) bands, have been studied for many cond itions of temperature (200-300 K), total pressure (0.5-10 atm), and mi xture (with He, Ar, O-2, and N-2) The theoretical approach used is bas ed on the Energy Corrected Sudden approximation; its parameters have b een deduced from both line-broadening data and measured absorption by the Q branches. Comparisons between experimental and computed spectra demonstrate the quality of the model, regardless of the conditions. De tailed analysis of the influences of the Q-lines spectral spacing, tem perature, total pressure, and collision partner are presented. They sh ow that significantly larger line-mixing effects are obtained when CO2 -He is considered with respect to CO2-(Ar,O-2,N-2) This is analyzed in terms of the relative contributions of the short-and midrange interac tion forces and of propensity rules resulting from the coupling of ang ular momenta. (C) 1997 American Institute of Physics.